As an example of a millimeter-wave band transmitter/receiver for transmitting and receiving signals in a millimeter-wave band, there is a video transmission system of a 50 GHz band described in “New Version of 50 GHz Simple Radio Equipment” (The 1997 IEICE General Conference C-2-123, pp. 178) (Literature 1).
The millimeter-wave band transmitter/receiver in Literature 1 includes a transmitter 1100 shown in FIG. 10A and a receiver 1150 shown in FIG. 10B. As will be described below, each of transmitter 1100 and receiver 1150 is constructed by a baseband section (indoor section) and a radio section (outdoor section).
Transmitter 1100 has: a baseband section including a modulator 1103 (indicated as “MOD for sound” in the diagram), a bandpass filter 1104 (indicated as “FIL” in the diagram), and analog/digital (A/D) converters 1109L and 1109R; and a radio section including a frequency modulator 1105, a frequency doubler 1107a (indicated as “x2” in the diagram), a frequency quadruplet 1107b (indicated as “x4” in the diagram), an amplifier 1108, and an antenna 1106.
The baseband section in transmitter 1100 multiplexes a video signal and a sound signal. Sound stereo signals (R and L) inputted from sound signal input terminals 1102L and 1102R are converted into digital signals by analog/digital converters 1109L and 1109R and the digital signals are modulated by modulator 1103. An output of modulator 1103 is combined with a video signal received from a video signal input terminal 1101 via bandpass filter 1104. In such a manner, a video transmission signal of one channel in the baseband is generated.
The generated video transmission signal is modulated by frequency modulator 1105 of a 6 GHz band included in the radio section. An output of frequency modulator 1105 is frequency-modulated by being multiplied by eight times via frequency doubler 1107a and frequency quadruplet 1107b and, further, the modulated signal is amplified via amplifier 1108. From antenna 1106, the generated millimeter-wave video transmission signal is radiated.
Receiver 1150 includes: a radio section including a local oscillator 1151, a down-converter 1152, an antenna 1156, and a frequency demodulator 1153 (indicated by “DEM” in the diagram); and a baseband section including a filter and distributor 1154 (indicated as “FIL” in the diagram), a sound demodulator 1155 (indicated as “DEM for sound” in the diagram), and digital/analog (D/A) converters 1157L and 1157R.
Down-converter 1152 down-converts a received video transmission signal on the basis of an output of local oscillator 1151 in the 50 GHz band. An IF (Intermediate Frequency) signal outputted from down-converter 1152 is demodulated by frequency demodulator 1153. A baseband signal is outputted from frequency demodulator 1153. The generated baseband signal is demultiplexed into a sound signal and a video signal via filter 1154. The sound signal is demodulated by demodulator 1155, thereby generating sound stereo signals (R and L). The video signal and sound stereo signals are supplied to a display device having a video terminal 1160 and sound terminals 1161L and 1161R.
Another example of the millimeter-wave band transmitter for transmitting signals in the millimeter-wave band, there is a transmitter for an HDTV (High Definition TV) adapted to the 60 GHz band described in “60-GHz-Band Ultracompact Transmitter for HDTV (1997 IEEE MTT-S Digest, pp. 1143-1146) (Literature 2). A transmitter 1200 of Literature 2 will be described by referring to FIGS. 11 and 12.
Transmitter 1200 in Literature 2 has three kinds of millimeter-wave transmitters 1210, 1220 and 1230. Transmitter 1200 receives video component signals (Y, Pb and Pr) as input signals. A luminance signal Y is inputted to millimeter-wave transmitter 1210 via an input terminal 1211, a color difference signal Pb is inputted to millimeter-wave transmitter 1220 via a terminal 1221, and a color difference signal Pr is inputted to millimeter-wave transmitter 1230 via a terminal 1231.
Millimeter-wave transmitter 1210 has a video amplifier 1212, a temperature compensator 1217, a frequency modulator 1213, a frequency quadrupler 1214 (indicated as “x4” in the diagram), a power amplifier 1215, and an antenna 1216. Millimeter-wave transmitter 1220 has a video amplifier 1222, a temperature compensator 1227, a frequency modulator 1223, a frequency quadrupler 1224, a power amplifier 1225 and an antenna 1226. Millimeter-wave transmitter 1230 has a video amplifier 1232, a temperature compensator 1237, a frequency modulator 1233, a frequency quadrupler 1234, a power amplifier 1235 and an antenna 1236.
Millimeter-wave transmitters 1210, 1220 and 1230 generate radio signals modulated in the millimeter-wave band and radiate the generated radio signals from antennas 1216, 1226 and 1236, and radiated signals Y, Pb and Pr are multiplexed in a space.
More specifically, millimeter-wave transmitters 1210, 1220 and 1230 amplify input video component signals to proper levels by video amplifiers 1212, 1222 and 1223, respectively. Outputs of video amplifiers 1212, 1222 and 1223 are inputted to frequency modulators 1213, 1223 and 1233 and frequency-modulated. The frequency of the frequency-modulated signal is multiplied by four by frequency quadruplers 1213, 1224 and 1234, thereby increasing frequency shift and modulated frequency of frequency modulation.
The modulated signals up-converted into millimeter waves are amplified by power amplifiers 1215, 1225 and 1235 and radiated from antennas 1216, 1226 and 1236. Millimeter-wave band modulated signals Y, Pb and Pr are combined to a video signal in space.
In the system of Literature 1, information which can be transmitted by a single transmitter/receiver is only one channel including a video image and sound. Therefore, in a house, video signals from a plurality of electronic devices and broadcast wave signals cannot be radio-connected. Specifically, TV (television) broadcast waves and video and sound signals from electronic devices such as a video, a DVD (digital versatile disc), a TV camera and a personal computer cannot be radio-connected simultaneously and independently in a house. Further, a plurality of such electronic devices cannot be carried to different rooms and used simultaneously at the different places.
Transmitter 1200 of Literature 2 transmits a video component signal for high definition TV. From transmitter 1200, video signals of three channels of the NTSC system can be transmitted. However, transmitter 1200 needs three kinds of transmission units. In the configuration of using three kinds of transmission units, when stability of the frequency of the frequency modulator fluctuates, stable demodulation cannot be performed on the reception side. Therefore, extremely stable frequency modulation is required.
In the configuration of transmitter 1200, however, a frequency modulator of a wide range is necessary for video signals and the frequency has to be shifted. Consequently, an oscillator of high stability cannot be used.
In transmitter 1200, temperature compensators 1217, 1227 and 1237 for frequency modulation of a broadband are provided. However, the frequency is basically stabilized by a dielectric resonator of 15 GHz band, and it is difficult to realize stable oscillation.
Further, to convert the modulation wave into millimeter-wave radio frequencies, the frequency is multiplied by four. As a result, frequency fluctuation in the modulation wave increases by four times, so that frequency stability is worsened in the radio frequency band of the millimeter waves. In addition, the electronic devices are vulnerable to mechanical fluctuations and power source voltage fluctuations, so that it is difficult to carry the devices to different rooms and use them.
The present invention therefore has been achieved to solve the problems and its object is to provide a radio communication device, a transmitter and a receiver corresponding to millimeter waves, capable of stably transmitting/receiving a plurality of different signal waves.